As is known, knitting machines with latch needles are generally equipped with sinkers which co-operate with the needles in forming knitting.
More particularly, sinkers perform the function of defining a knitting forming plane on which the portion of knitting arranged between two contiguous needles rests while such needles, after picking up the yarn at a feed or drop of the machine, retract into the needle holder in order to form a new loop of knitting and to lower the previously formed loop of knitting and of tensioning the loop of knitting on the shank of the needle while said needle is extracted with its tip and with part of its shank from the needle holder of the machine in order to pick up the yarn dispensed at a feed or drop of the machine and form a new loop of knitting. The engagement of the sinkers with the knitting that tensions the loop of knitting on the shank of the needle, in this step, also prevents the loop of knitting from following the needle in its extraction movement and assuredly achieves the opening of the latch and the passage of the loop of knitting below the latch. The tensioning of the loop of knitting on the shank of the needle by the sinkers is generally assisted by traction of the already-formed knitted fabric, which is performed generally by means of pneumatic traction devices in small-diameter circular machines and by means of mechanical devices in other machines.
The sinkers are usually accommodated in appropriately provided slots defined, at the end of the needle holder from which the needles protrude in order to pick up the yarn at a feed or drop of the machine, directly in the needle holder or in a supporting element which is fixed to the needle holder. The sinkers are generally actuated by means of appropriately provided cams, which face the region of the needle holder that accommodates the sinkers and form paths which can be engaged by heels of the sinkers, which protrude from the needle holder, as a consequence of a movement of the needle holder with respect to the cams.
In many types of fine-gauge knitting machines, in which the space between the needles is very small, the sinkers are absent.
In these machines, the absence of the sinkers, imposed by space occupation requirements, is the source of problems and drawbacks. The absence of the sinkers, during accidental breakage of the yarn being knitted, in fact prevents automatic resumption of the formation of knitting and forces manual intervention in order to unload the new loops of knitting onto the shank of the needles which, as a consequence of the breakage of the yarn, have lost the knitting.
Moreover, due to the fact that in these machines the tensioning of the loops of knitting on the shank of the needles while such needles are extracted with their tip from the needle holder to pick up the yarn at a feed or drop of the machine is performed exclusively by the fabric traction device, such tensioning can be insufficient, also due to the large number of needles engaged with the knitting, to ensure the passage of the loops of knitting below the latch of the needles while the needles are extracted from the needle holder, causing knitting errors.
In order to limit these problems, in some cases these machines are actuated by moving to knit in each instance, at a feed or drop of the machine, only one needle every two contiguous needles, so that the needle that is not used to form knitting performs a retaining action on the loops of knitting formed by the contiguous needles that are moved to knit. This refinement, however, suffers the drawback of not allowing to exploit fully the production potential of the machine.
In order to solve these problems, it has been proposed to provide machines with knitting retainers which are arranged in the slots of the needle holder laterally to the corresponding needle and are provided with a portion which protrudes beyond the knitting forming plane. These knitting retainers can be actuated in order to engage, between two contiguous needles, the loop linking portion, so as to retain it as an alternative to the sinkers.
However, this refinement can be adopted only in reduced-gauge machines, since in fine-gauge machines, due to space occupation reasons, the knitting retainers would have to be so thin as to be exposed to easy deformations during operation, which would compromise their integrity and reliability.